1. Field of the Invention
The present invention relates generally to a wireless communication system. More particularly, the present invention relates to an apparatus for receiving wideband Radio Frequency (RF) signals, and a method for controlling the same.
2. Description of the Related Art
For transmission of mass multimedia, communication systems require wider signal bandwidths. In addition, to improve flexibility, the communication systems should support not only a certain operator's band but also a wide frequency band.
A receiver in the typical communication system removes unnecessary signals from an operator's band by filtering a signal received via an antenna using an RF front-end filter. The signal, which has passed the RF front-end filter, is mixed with a Local Oscillator (LO) signal generated in a Phase Locked Loop (PLL) by a mixer, thereby being down-converted into an Intermediate Frequency (IF) signal. However, signals that were not removed in the RF front-end filter may still affect the received signal. In particular, a half IF serves as interference to the received signal due to second harmonic signals caused by nonlinearity of the mixer.
FIG. 1 shows a characteristic of an RF front-end filter in a communication system using an operator's band according to the related art.
Referring to FIG. 1, a signal 104 of a received-signal frequency fSG is down-converted into a signal of an IF fIF by being mixed with a signal of a local signal frequency fLO generated in a PLL. Because a bandwidth 102 of the RF front-end filter, which passes only the signals in the operator's band, is sufficiently narrow, only the signal 104 of the received-signal frequency fSG can pass the RF front-end filter, and an interference signal 106 having a half IF (fSG−fIF/2) is removed. The signal 106 of a half IF is removed in the RF front-end filter, preventing degradation of the received signal.
FIG. 2 shows a characteristic of an RF front-end filter in a communication system using a wideband according to the related art.
Referring to FIG. 2, because of the wide pass bandwidth 202 of the RF front-end filter, not only a received-signal frequency fSG but also a half IF (fSG−fIF/2) may pass through the RF front-end filter.
The half IF has a characteristic defined by Equation (1) below.
                              Half_IF          =                                                    f                SG                            -                                                f                  IF                                2                                      =                                                            f                  SG                                +                                  f                  LO                                            2                                      ⁢                                  ⁢                                                                              f                  SG                                +                                  f                  LO                                            2                        -                          f              Lo                                =                                                                      f                  SG                                -                                  f                  LO                                            2                        =                                          f                IF                            2                                      ⁢                                  ⁢                                            2              ×                                                                    f                    SG                                    +                                      f                    LO                                                  2                                      -                          2              ×                              f                LO                                              =                                                    f                SG                            -                              f                LO                                      =                          f              IF                                                          (        1        )            
As described above, when at least one term having a degree of 2 or more is additionally generated due to the nonlinearity of a mixer, an interference signal of a half IF is located at fIF as it passes the mixer, resulting in degradation of demodulation performance and thus reducing the overall reception performance of the system. To solve this half IF problem, technologies using a dual-IF structure and the like have been released conventionally, but these technologies may be complex in structure.